The practice of female sterilization as a method of fertility control began in Puerto Rico in the early thirties and increased rapidly during the next three decades. Studies carried out in 1965 and in 1968 revealed that more than one third of all women ever married in the ages between 20 and 49 years had been sterilized. Thus, Puerto Rico is by far the country with the highest rate of female sterilization of the world. For this reason it offers an unique opportunity to determine the demographic effectiveness of this method of fertility control. This determination is the main objective of the proposed study. Another important objective of this project is to determine the impact that the increased utilization of the contraceptive pill has had in the trends and patterns of female sterilization in Puerto Rico. To fulfill these objectives an island-wide sample of 2,028 women 15 and 54 years of age will be used. These were interviewed during the summer of 1976. The data obtained include personal characteristics, a pregnancy history, a marital history and experience in the use of contraceptive methods. The average number of children of sterilized women will be compared against those not sterilized to analyze the effect of sterilization on fertility. Age of women, age at first marriage, duration of marriage and use of other contraceptive methods are among the control variables to be utilized in this comparison. A correlation analysis in which fertility (children ever born) will be the dependent variable will also be undertaken. In this analysis several variables related to sterilization will be considered as the independent ones (whether or not sterilized, proportion of years sterilized of total years marriage, etc.).